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Wingbeat Frequency

Because the bird in the Luneau video flies with rapid, steady
wingbeats, we compared its wingbeat frequency with that of known
Pileated Woodpeckers and with a measurement of wingbeat frequency from
a known Ivory-billed Woodpecker.

The bird in the Luneau video flies in a straight, direct “beeline”
flight without changing its wingbeat frequency for 4.5 sec before
disappearing among the trees. This direct, powerful, straight-line
flight is described by many who see the video for the first time as
“duck-like.” Indeed, the bird in the Luneau video
flies with rapid wingbeats in a direct path for the entire time it is
in view, completing 8 fully visible wingbeats in about 0.9 seconds, and
10 wingbeats (including two somewhat obscured ones) in about 1.2
seconds. Such escape behavior is extremely unusual among
Pileated Woodpeckers, which typically change from a few rapid
wingbeats to a slower, swooping or bounding flight soon after leaving
their perch. Based on a standard video rate of 29.97 frames per second,
we can calculate the wingbeat frequency of the Luneau video bird as
follows: using the position where the wings are over the back forming
an acute 'V' as an index point for each of eight wingbeats, we observe
this position in fields 250 ("0"), 366.7 ("1"), 483.3 ("2"), 583.3
("3"), 700 ("4"), 816.7 ("5"), 950 ("6"), 1066.7 ("7"), and 1183.5
("8"). These eight wingbeats span 56 video fields. At 59.94 fields per
second, this corresponds to 8 beats in 0.934 seconds, or a wingbeat
frequency of 8.6 beats per second.

The wingbeat frequencies of Pileated Woodpeckers in our videos from
Arkansas are 2-4 beats per second in level flight (many examples) and
4-7.5 beats for short periods during hasty departures (n = 5). Moreover, experts who have
studied Pileated Woodpecker flight using video analysis timed the
fastest departures at 7 beats per sec (Tobalske 1996, personal
communication). Thus, wingbeat frequency of the woodpecker in the
Luneau video is faster than any recorded Pileated Woodpecker.

Remarkably, in part of the historic audio recording of a pair of
Ivory-billed Woodpeckers at their nest, the wingbeats of one of the
birds flying rapidly from the tree are clearly audible. In this 1935
recording of Ivory-billed Woodpeckers interacting at the nest
hole, kent, kent, kent calls are followed by the
sound of 8 distinct wingbeats as one Ivory-billed Woodpecker departs from the
tree. Tanner described Ivory-billed Woodpecker flight as powerful and
unusually noisy.Listen to the recording.

The wingbeat sounds recorded by Arthur Allen and Peter Paul Kellogg
in 1935 can be plotted on a sonogram and counted; their frequency is
8.4 beats per second. The frequency of the woodpecker’s take-off flight
in the Luneau video is almost identical: 8.6 beats per second.

Sound spectrogram of wingbeats of an ivory-billed
woodpecker taking flight, recorded in 1935 at the Singer Tract in Louisiana. The
seven wingbeat cycles have a total duration of 836 ms, for an average period of
119 ms, and an average wingbeat rate of 8.4 beats/s.